Nintendo Switch will have its online services being worked on next week, and Nintendo has given us a window in which to expect interruptions of service while they maintain their network.
Server maintenance is set to happen on Wednesday, August 9 from 8:50 PM ET to around 10:30 PM ET. According to their website, "some network services may become unavailable."
As always, details aren't given on the maintenance. This is pretty standard for Nintendo, but the good thing is, this maintenance doesn't happen until Splatoon 2 finishes up its new event, Splatfest, which began yesterday, so it will go off without any interruptions.
Splatoon 2 recently received an update that fixed a number issues with the otherwise well-received sequel.